To increase power handling capability of power electronic circuits, power semiconductor devices are often connected in parallel by wire bonding devices within a package. However, although wire bonding devices within a package results in much less stray inductance than that resulting from interconnecting discrete devices, the stray inductance is still too high for high-frequency operation. In particular, such stray inductance causes ringing in both device current and voltage in addition to unequal current sharing among parallel-coupled devices.
Radio frequency packages are available that minimize inductance by making the metal leads of the packaged device, or die, as wide as possible. Some packages also enhance the gate drive through a separate, wide return connection from the die known as a Kelvin lead. Disadvantageously, however, the size of such leads limits such packages to a single device. Hence, connecting multiple devices within such packages is impossible. Therefore, half-bridge and full-bridge circuits require the interconnection of multiple device packages, adding stray inductance thereto.
Commonly assigned U.S. Pat. No. 5,043,859 of C. S. Korman et al., issued Aug. 27, 1991 and incorporated by reference herein, describes a low-inductance, half-bridge package including an insulating substrate having first, second and third external power terminals along with control terminals bonded to the substrate. The power terminals are configured to provide a current path straight through the package from the first power terminal to the second (or common) power terminal and from the second power terminal to the third power terminal. The control terminals each preferably comprise pairs of Kelvin terminals in order to minimize feedback from the power current paths to the control circuits. The power devices are bonded to the first and second power terminals, respectively, and have connections to the second and third power terminals, respectively. For single upper and lower half-bridge devices, the package of U.S. Pat. No. 5,043,859 is thus configured to have very low stray inductance for high-frequency operation. However, if multiple devices are coupled in parallel in a half-bridge package such as that of U.S. Pat. No. 5,043,859, the wire bonding length for each power device is different, resulting in an undesirable level of stray inductance which causes unequal current sharing and unequal delays in the devices.
Accordingly, it is desirable to provide an improved low-inductance package for multiple paralleled devices suitable for use in half-bridge and full-bridge circuit configurations.